Aluminum fluoride flux synthesis method for producing cerium doped YAG

Abstract

A method of making a YAG:Ce 3+ phosphor includes adding an AlF 3 fluxing agent to a yttrium, cerium, aluminum and oxygen containing starting powder and sintering the powder in a weak reducing atmosphere generated by evaporating charcoal. The resulting phosphor has a luminosity of greater than 435 lumens per watt.

What is claimed is:  
     
       1. A phosphor comprising: 
       
         
           A 3 D 5 E 12 :Ce 3+ ,  
         
       
       wherein 
       A comprises at least one of Y, Gd, Lu, Sm and La;  
       D comprises at least one of Al, Ga, Sc and In;  
       E comprises oxygen;  
       Y, Al and oxygen comprise a crystal lattice of the phosphor; and the phosphor luminosity is greater than 435 lumens per watt.  
     
     
       2. The phosphor of  claim 1 , wherein: 
       the phosphor luminosity is 435 to 453 lumens per watt;  
       the phosphor x color coordinate ranges from 0.435 to 0.446; and  
       the phosphor y color coordinate ranges from 0.537 to 0.545.  
     
     
       3. The phosphor of  claim 2 , comprising: 
       (Y 1−x−z Ce x Gd z ) 3 Al 5 O 12 , wherein 0.1>x>0 and 0.05>z≧0.  
     
     
       4. The phosphor of  claim 3 , comprising: 
       (Y 0.97 Ce 0.03 ) 3 Al 5 O 12 , wherein:  
       the phosphor luminosity is 453 lumens per watt;  
       the phosphor x color coordinate is 0.435; and  
       the phosphor y color coordinate is 0.545.  
     
     
       5. The phosphor of  claim 3 , comprising (Y 0.93 Gd 0.05 Ce 0.03 ) 3 Al 5 O 12 , wherein: 
       the phosphor luminosity is 441 lumens per watt;  
       the phosphor x color coordinate is 0.446; and  
       the phosphor y color coordinate is 0.537.  
     
     
       6. The phosphor of  claim 3 , wherein at least a portion of the oxygen is substituted by fluorine from an AlF 3  flux. 
     
     
       7. A white light illumination system comprising a light emitting diode and the phosphor of  claim 1 . 
     
     
       8. The system of  claim 7  wherein the light emitting diode contains at least one semiconductor layer comprising GaN, ZnSe or SiC having an emission wavelength greater than 400 nm but less than 500 nm. 
     
     
       9. The system of  claim 7 , further comprising a shell containing the light emitting diode and an encapsulating material between the shell and the light emitting diode, and wherein: 
       a) the phosphor is coated over a surface of the light emitting diode;  
       b) the phosphor is interspersed in the encapsulating material; or  
       c) the phosphor is coated onto the shell.  
     
     
       10. A method of making a YAG:Ce 3+  phosphor, comprising: 
       combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF 3  to obtain a first mixture; and  
       heating the first mixture to form a solid YAG:Ce 3+  phosphor body, wherein the phosphor luminosity is greater than 435 lumens per watt.  
     
     
       11. The method of  claim 10 , wherein the YAG:Ce 3+  phosphor comprises: 
       
         
           A 3 D 5 E 12 :Ce 3+ ,  
         
       
       wherein 
       A comprises at least one of Y, Gd, Lu, Sm and La;  
       D comprises at least one of Al, Ga, Sc and In;  
       E comprises oxygen; and  
       Y, Al and oxygen comprise a crystal lattice of the phosphor.  
     
     
       12. The method of  claim 11 , wherein the phosphor comprises: 
       (Y 1−x−z Ce x Gd z ) 3 Al 5 O 12 , wherein 0.1>x>0 and 0.7>z≧0; and  
       further comprising fluorine incorporated from the AlF 3 .  
     
     
       13. The method of  claim 11 , wherein: 
       the at least one powder comprises a first powder comprising yttrium and oxygen, a second powder comprising cerium and oxygen, and a third powder comprising aluminum and oxygen; and  
       AlF 3  comprises a fourth powder.  
     
     
       14. The method of  claim 13 , wherein: 
       the first powder comprises Y 2 O 3 ;  
       the second powder comprises CeO 2 ; and  
       the third powder comprises Al 2 O 3 .  
     
     
       15. The method of  claim 13 , wherein the at least one powder further comprises a Gd 2 O 3  powder. 
     
     
       16. The method of  claim 13 , wherein at least one of the first powder, the second powder and the third powder comprises an oxalate, hydroxide, carbonate or nitrate compound. 
     
     
       17. The method of  claim 11 , wherein the concentration of the fourth powder comprises between 2 and 20 mole percent per mole of the phosphor produced. 
     
     
       18. The method of  claim 11 , wherein the step of combining at least one powder comprises: 
       dissolving Y and Ce in an acid;  
       co-precipitating a first powder comprising Y, Ce and oxygen with oxalic acid; and  
       combining the first powder with an Al 2 O 3  powder and an AlF 3  powder.  
     
     
       19. The method of  claim 18 , further comprising: 
       dissolving Gd in the acid; and  
       wherein the first powder further comprises Gd.  
     
     
       20. The method of  claim 10 , wherein the step of heating comprises sintering in a reducing atmosphere comprising carbon. 
     
     
       21. The method of  claim 20 , wherein the reducing atmosphere does not contain forming gas. 
     
     
       22. The method of  claim 20 , wherein the step of sintering comprises: 
       placing the first mixture into a first container; and  
       evaporating a carbon based fuel to obtain the reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide.  
     
     
       23. The method of  claim 22 , further comprising: 
       placing the carbon based fuel into a second container, wherein the carbon based fuel comprises activated charcoal;  
       placing the first container comprising a covered alumina crucible into the second container; and  
       raising the temperature of the second container to 1500° C. for 6 hours.  
     
     
       24. The method of  claim 22 , wherein the step of heating comprises raising the temperature of the first container to 1000 to 1600° C. for 2 to 10 hours. 
     
     
       25. A method of using a phosphor, comprising: 
       converting the solid phosphor body made by the process of  claim 11  to a phosphor powder; and  
       placing the phosphor powder into an illumination system.  
     
     
       26. The method of  claim 25 , wherein the step of converting comprises at least one of dry milling, wet milling, jet milling or crushing. 
     
     
       27. The method of  claim 25 , wherein the step of placing the phosphor powder into the illumination system comprises placing the phosphor powder into a white light illumination system containing a light emitting diode, into a plasma display or into a fluorescent lamp. 
     
     
       28. The method of  claim 27 , wherein the step of placing the phosphor powder into a white light illumination system comprises: 
       a) coating a suspension of the phosphor powder and a solvent over a surface of the light emitting diode and drying the suspension;  
       b) interspersing the phosphor powder in an encapsulating material overlying the light emitting diode; or  
       c) coating a suspension of the phosphor powder and a solvent onto a shell enclosing the light emitting diode and drying the suspension.  
     
     
       29. The method of  claim 27 , wherein the step of placing the phosphor powder into a plasma display or into a fluorescent lamp comprises: 
       coating a suspension of the phosphor powder and a solvent onto a surface of a lamp cover or onto a surface of a portion of a plasma display; and  
       drying the suspension.  
     
     
       30. The method of  claim 10 , wherein: the step of combining comprises: 
       a) combining a Y 2 O 3  powder, a CeO 2  powder and an Al 2 O 3  powder with AlF 3  to form a first mixture; or  
       b) dissolving Y and Ce in an acid, co-precipitating a first powder comprising Y, Ce and oxygen, and combining the first powder with an Al 2 O 3  powder and an AlF 3  powder to form a first mixture; or  
       c) combining yttrium, cerium and aluminum containing compounds selected from at least one of oxide, oxalate, hydroxide, carbonate and nitrate compounds with AlF 3  to form a first mixture;  
       the step of heating comprises: 
       a) placing the first mixture into a crucible;  
       b) raising the temperature of the crucible to 1000 to 1600° C. for 2 to 10 hours; and  
       c) supplying a reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide into the crucible by evaporating activated charcoal to form a solid phosphor body comprising (Y 1−x−z Ce x Gd z ) 3 Al 5 (O,F) 12 , wherein 0.1>x>0 and 0.7>z≧0; and  
       further comprising converting the solid phosphor body into a phosphor powder.  
     
     
       31. The method of  claim 30 , wherein the step of combining comprises: combining a Y 2 O 3  powder, a CeO 2  powder and an Al 2 O 3  powder with AlF 3  to form a first mixture. 
     
     
       32. A phosphor powder made by the process of  claim 11 . 
     
     
       33. An illumination system comprising a fluorescent lamp, a plasma display or a light emitting diode and the phosphor powder of  claim 32 . 
     
     
       34. A method of making a YAG:Ce 3+  phosphor, comprising: 
       combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF 3  to obtain a first mixture; and  
       sintering the first mixture in a reducing atmosphere comprising carbon to form a solid YAG:Ce 3+  phosphor body.  
     
     
       35. The method of  claim 34 , wherein the reducing atmosphere does not contain forming gas. 
     
     
       36. The method of  claim 34 , wherein the step of sintering comprises: 
       placing the first mixture into a first container; and  
       evaporating a carbon based fuel to obtain the reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide.  
     
     
       37. The method of  claim 36 , further comprising: 
       placing the carbon based fuel into a second container, wherein the carbon based fuel comprises activated charcoal;  
       placing the first container comprising a covered alumina crucible into the second container; and  
       raising the temperature of the second container to 1500° C. for 6 hours.  
     
     
       38. The method of  claim 36 , wherein the step of sintering comprises raising the temperature of the first container to 1000 to 1600° C. for 2 to 10 hours. 
     
     
       39. The method of  claim 34 , wherein the YAG:Ce 3+  phosphor comprises: 
       
         
           A 3 D 5 E 12 :Ce 3+ ,  
         
       
       wherein 
       A comprises at least one of Y, Gd, Lu, Sm and La;  
       D comprises at least one of Al, Ga, Sc and In;  
       E comprises oxygen;  
       Y, Al and oxygen comprise a crystal lattice of the phosphor; and  
       wherein the phosphor luminosity is greater than 435 lumens per watt. 
     
     
       40. The method of  claim 39 , wherein: 
       the phosphor luminosity is 435 to 453 lumens per watt;  
       the phosphor x color coordinate ranges from 0.435 to 0.446; and  
       the phosphor y color coordinate ranges from 0.537 to 0.545.  
     
     
       41. The method of  claim 39 , wherein the step of combining comprises: 
       combining a Y 2 O 3  powder, a CeO 2  powder and an Al 2 O 3  powder with AlF 3  to form the first mixture.  
     
     
       42. A method of making a phosphor comprising: combining at least one powder comprising yttrium, cerium, aluminum and oxygen with AlF 3  to obtain a first mixture, wherein the step of combining comprises: 
       a) combining a Y 2 O 3  powder, a CeO 2  powder and an Al 2 O 3  powder with AlF 3  to form a first mixture; or  
       b) dissolving Y and Ce in an acid, co-precipitating a first powder comprising Y, Ce and oxygen, and combining the first powder with an Al 2 O 3  powder and an AlF 3  powder to form a first mixture; or  
       c) combining yttrium, cerium and aluminum containing compounds selected from at least one of oxide, oxalate, hydroxide, carbonate and nitrate compounds with AlF 3  to form a first mixture;  
       heating the first mixture to form a solid phosphor body, wherein the step of heating comprises: 
       a) placing the first mixture into a crucible;  
       b) raising the temperature of the crucible to 1000 to 1600° C. for 2 to 10 hours; and  
       c) supplying a reducing atmosphere comprising at least one of carbon monoxide and carbon dioxide into the crucible by evaporating activated charcoal to form a solid phosphor body comprising (Y 1−x−z Ce x Gd z ) 3 Al 5 (O,F) 12 , wherein 0.1>x>0 and 0.7>z≧0; and  
       further comprising converting the solid phosphor body into a phosphor powder.  
     
     
       43. The method of  claim 42 , wherein the step of combining comprises: 
       combining a Y 2 O 3  powder, a CeO 2  podwer and an Al 2 O 3  powder with AlF 3  to form the first mixture.